Different mechanisms may be used for controlling a wireless transmit/receive unit (WTRU)'s network access when the network is congested. Such mechanisms may include, for example, access class barring (ACB), extended access barring (EAB) and service specific access control (SSAC).
According to ACB, at subscription, one or more access classes may be allocated to a subscriber and stored in the subscriber's universal subscriber identity module (USIM). Regular WTRUs may be randomly assigned an access class (AC) (e.g., from 0-9), but some “special” WTRUs may be assigned a higher priority AC (e.g., 11-15). Access-class-based-barring-information may be broadcast in the system information (SI), for example, which may control the mean access barring time and the percentage of barred accesses. When a WTRU attempts to initiate an access, it may attempt to draw a random number and compare the random number to an ac-BarringFactor, which may be a part of the broadcast AC barring information. If the random number is greater than the ac-BarringFactor, the access may be barred for a period of a calculated mean barring time.
EAB may be targeted for WTRUs that are configured to be subject to EAB control, such as WTRUs that are of lower priority or that are delay-tolerant (e.g., machine-type-communication (MTC) devices). Before initiating an access, the non-access stratum (NAS) may first determine whether the access is subject to EAB control based on at least one criterion, such as a WTRU's roaming category, the nature of the access, or whether the WTRU belongs to a special AC (e.g., 11-15). If the WTRU is determined to be subject to EAB control, the NAS may compare the WTRU's AC with a broadcast EAB barring-bitmap (e.g., where each bit represents the barring-status of an AC, such as AC 0-9). There may be no barring factor or barring time defined in the EAB parameters.
SSAC is based on ACB but may have a different set of dedicated SSAC barring parameters, which may differentiate multi-media telephony (MMTEL)-voice service and MMTEL-video service using a different barring factor and/or barring time. Based on broadcast ssac-barring configurations and a WTRU's AC, the WTRU may determine the real barring parameters and inform the upper service layer. Before initiating the service, the service layer may draw a random number and compare it against the barring parameters to determine whether or not the service is barred.